Prototype Pattern

In this article I would like to explain the Prototype Pattern and C# support for it. The prototype pattern provides an alternative to instantiating new objects by copying the prototype of an existing one.

Challenge

You are working on an application having setting stored in class Settings. The properties of the class are assignedinside the constructor. It involves calling the configuration file, security database, user profile database etc.

You need to pass the above instance to a component inside a library. The component could play around with the properties so we need to send only another instance of Settings. As the instance creation is expensive we need to create a copy of the above instance.

What would be the best approach?

Definition

“Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype”

Solution

We can use the Prototype pattern to address this scenario. This pattern allows us to create a new instance by prototyping an existing instance with required properties.

The System.object class includes new method named MemberwiseClone() which provides a shallow copy of the current object. Shallow copy involves copying only the value types. Coupled with ICloneable interface we can provide a Clone() method that invokes MemberwiseClone() for the Settings class.

publicclassSettings : ICloneable

{

public Settings()

{

// Load ApplicationSettings from Configuration

// Load ThemeSettings from Database

// Load UserSettings from Database

Thread.Sleep(3000); // Simulate a delay for the above operations

ApplicationSettings = “ApplicationSettings1”;

ThemeSettings = “ThemeSettings1”;

UserSettings = “UserSettings1”;

}

publicstringApplicationSettings

{

get;

set;

}

publicstringThemeSettings

{

get;

set;

}

publicstringUserSettings

{

get;

set;

}

publicobject Clone()

{

returnthis.MemberwiseClone();

}

publicoverridestringToString()

{

returnthis.ApplicationSettings + ” ” +

this.ThemeSettings + ” ” +

this.UserSettings;

}

}

Executing the Application

Now we can try playing with the class instances. First we create an instance of Settings (which is a 3 second delay process). Later we take a clone of the Settings instance and modify the properties. We can see that the new instance was created using Clone() method.